During operation, a rolling bearing that e.g. is well lubricated, properly aligned and sufficiently protected from effects of abrasive or moisture during operation may still fail from rolling contact fatigue. This type of failure is normally observed as flaking off of metallic particles from surface of the raceway of an inner or outer ring of a bearing, or from the surface of the rolling elements. The flaking typically commences as a sub-surface crack below the surface which propagates to the surface whereat a pit or a spall is formed in the surface exerted to the load.
To improve the use and benefit of rolling bearings, it is important to be able to predict length of service, life, endurance, that can be achieved from a bearing in a specific application. However, due to the rolling contact fatigue, the ability to make this type of predictions is hampered.
In order to predict bearing fatigue parameters, statistical procedures have been established for e.g. theoretical life predictions of bearing fatigue life. Such predictions, using e.g. Weibull statistics, are based on large quantities of data which are collected by experimental techniques encompassing large populations of apparently identical rolling bearings which are subjected to apparently identical load, speed, lubrication and environmental conditions.
Methods for testing life, or endurance, parameters of bearings are further used to evaluate and assess the bearing material and manufacturing processes of bearings, such as surface forming and heat treatment processes. However, the assessment of initiation and development of sub-surface initiated fatigue in rolling contact applications is time consuming, costly and difficult to measure and predict due to e.g. the spread in experimental fatigue data. Known methods that are used encompass large expenditures and time in order to evaluate the usefulness of steels intended for bearing steel component production, and all of these methods are hampered by the use of numerous bearings that are tested under conditions that are beyond the actual conditions of specific applications. In other words, even though accelerated techniques are utilized, a large amount of bearings must be tested for relatively long times in order to achieve valid estimates of bearing life, wherein the testing costs are closely linked to the manufacturing cost of the bearing test specimens.